On Thu, Jun 23, 2011 at 11:06 AM, John Fettig <john.fettig at gmail.com> wrote: > On Thu, Jun 23, 2011 at 11:03 AM, Jed Brown <jed at 59a2.org> wrote: >> On Thu, Jun 23, 2011 at 16:59, John Fettig <john.fettig at gmail.com> wrote: >>> >>> I understand everything you say here except what "compressing" means. >>> It is compressed by virtue of being in CSR format, but then you do >>> some additional mapping with the column indices that further >>> compresses it? What purpose does changing the column indices serve? >> >> It operates on the dense vector consisting of only those entries on other >> processors that interact with the current one. If this thing operated on the >> full global vector, there would either need to be a matrix format that could >> operator on "sparse vectors" (i.e. an additional layer of indirection) or >> the whole dense global vector would need to be gathered to every process >> which would be horribly non-scalable. > > Thanks for the explanation, it makes sense.
Is there any way to access the map from global numbering to the compressed numbering? John
